In order to forge workpieces with a distinct longitudinal axis, forging machines are used which have three or more rams arranged at different angles in one plane, and in particular four rams which are arranged offset at 90.degree. to one another in a cruciform manner. The rams act radially upon the workpiece, which is guided longitudinally in the system axis, and are equipped with tools. It is structurally advantageous if the rams, which are guided in the machine frame, are constructed, at their ends remote from the tools (or dies), in the form of cylinders of piston-cylinder units open towards the outside, or are connected to such piston-cylinder units.
Because of the considerable forming capacity of these radial-forming forging machines, a high degree of enclosure, up to complete encirclement, of the workpiece has to be provided in the forming region. To this end, the tools should form a closed pass contour in the inner end position of the stroke, which position is adjustable. This is achieved in that either the tools are transversely displaceable in their common plane by means of tool supports on the rams and the part of the tool operating face exceeding the pass-contour dimension is covered by a lateral face of an adjacent tool, the tools being set accordingly by displacement devices acting upon the supports (U.S. Pat. Nos. 4796456, 4813263, and 4831864 corresponding to (EP 0228030 B1), or replaceable tools of suitable width are used (Peter Metzger, "Die numerisch gesteuerte Radial-Umformmaschine und ihr Einsatz im Rahmen einer flexiblen Fertigung" [The numerically controlled radial forming machine and its use in the framework of flexible finishing], Vol. 55 of Reports from the Institute for Forming Technology of the University of Stuttgart, published by Springer-Verlag, Berlin-Heidelberg-New York, 1980, pp. 36-39, 67-69, 112, 113, 129).
For a forging machine which is to be used for open-die fine forging it is recommended that the piston-cylinder units should be dimensioned in accordance with the operating stroke of the ram in order to minimise the compression volume, this being an essential pre-condition for rapid-stroke operation. The stroke position, by which the pass contour bounded by the tools is determined, can be set by adjustment of crossheads which are displaceable on the machine frame and support the pistons of the piston-cylinder units.